The invention relates to a turboprop engine having an inlet opening provided in the engine cage for cooling air for the cage interior and for an air/liquid heat exchanger arranged in this interior, having a cooling air delivery device as well as having an air guiding duct which accommodates the liquid/air heat exchanger and carries away the heat exchanger exhaust air.
Such a turboprop engine is known from U.S. Pat. No. 2,593,541. In this case, the air flow provided for an air oil cooler arrives directly from an inlet opening in the engine cage at the air oil cooler. The oil cooler exhaust air is carried away by way of the turbine exhaust air duct, the corresponding introduction device of the cooling air flow into the turbine exhaust air duct being constructed in the form of an ejector so that a cooling air delivery device is provided in the shape of this ejector. Such a cooling air delivery device is useful for those operations of the turboprop engine in which an aircraft equipped with this engine rolls along on the ground, particularly if a rolling along in the reverse direction takes place.
Another turboprop engine having a liquid-air heat exchanger, particularly an air oil cooler, is illustrated in European Patent Document EP 0 514 119 A1. Here, the air oil cooler is arranged in the area of the inlet opening so that the cooling of the cage interior takes place by means of the oil cooler exhaust air flow. In this case, the oil cooler exhaust air flows around the assemblies to be cooled which are arranged in the engine cage and is then also carried off by way of the turbine exhaust air duct, again the corresponding introduction device of the cooling air flow into the turbine exhaust air duct being constructed in the shape of an ejector.
At high exterior temperatures, for example, the oil cooler exhaust air flow can assume such high temperatures that the assemblies arranged in the engine cage which are acted upon by this air flow may be damaged.
It is an object of the invention to indicate measures by which an assembly arranged in the engine cage can be reliably cooled and in the process a sufficiently intensive air flow is guided through the liquid/air heat exchanger.
The achieving of this object is characterized in that the cooling air inlet opening is adjoined by an air guiding duct which is directed to at least one assembly to be cooled, and in that the cooling air delivery device is constructed as a fan which is disposed in front of the heat exchanger and is arranged in the air guiding duct.
In that the heat exchanger or oil cooler is arranged away from the inlet opening and a cooling air delivery device is provided which is constructed as a fan, the cooling air flow arriving through the inlet opening in the cage interior can first optimally act upon the assemblies to be cooled and will only then arrive on the oil cooler. From this oil cooler, this then heated air flow is carried away as the oil cooler exhaust air flow in a targeted manner, specifically by way of an air guiding duct so that any heating of the cage interior by the oil cooler exhaust air is virtually excluded.
In order to, in the process, guide the cooling air flow, which arrives in the engine cage by way of the inlet opening and which, because of the fan, is definitely of a sufficient intensity, in a targeted manner to the assemblies to be cooled, the air inlet opening is adjoined by an appropriately designed air guiding duct. In this air guiding duct or generally at the cooling air inlet opening, a separating device for water and/or particles, which may damage the cage interior, may also be provided.
The cooling air delivery device constructed as a fan can be driven by an electric motor, which has the advantage that, in a simple manner, only at a few operating points, specifically when a separate cooling air delivery is required at all, the required fan power must be provided. Since, however, a corresponding electric motor also results in an increased weight, the fan can also be driven mechanically by way of the so-called gear box, that is, by way of the transmission arrangement for the auxiliary unit drive of the flight gas turbine known to the person skilled in the art. Here, it is recommended to arrange a shifting coupling between the fan as well as the corresponding gear box output shaft in order to again only have to drive the fan if the delivery of a cooling air flow is required.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.